qxl_image.c: fix compilation break
qxl_image.c: fix compilation break

Since 3d511c30206bd8c9a207c436186a03af0bb02962 Xspice building is broken
due to undefined MAX_RELOCS when not building with XF86DRM_MODE.

fgouget/xf86-video-qxl,fgouget/xf86-video-qxl,fgouget/xf86-video-qxl,fgouget/xf86-video-qxl